I have to admit that I don't read Matthew 25:31-46 in exactly the same way jar. I can see your point about non-believers being included in with the sheep -- because they beleived in Christ by their actions.
But, on the other hand, I think you take too much liberalities with the text when presenting the goats as being almost exclusively Christian. I do see that Christians can be included in that group, and some most certainly will be. But I don't see it to the level you are stressing.
There are other passages of Scripture which allude to what you are saying, such as the one in which a tree is known by its fruit:
NIV writes:
"Watch out for false prophets. They come to you in sheep's clothing, but inwardly they are ferocious wolves. By their fruit you will recognize them.
Do people pick grapes from thornbushes, or figs from thistles?
Likewise every good tree bears good fruit, but a bad tree bears bad fruit. A good tree cannot bear bad fruit, and a bad tree cannot bear good fruit. Every tree that does not bear good fruit is cut down and thrown into the fire. Thus, by their fruit you will recognize them.
"Not everyone who says to me, 'Lord, Lord,' will enter the kingdom of heaven, but only he who does the will of my Father who is in heaven.
Many will say to me on that day, 'Lord, Lord, did we not prophesy in your name, and in your name drive out demons and perform many miracles?'
Then I will tell them plainly, 'I never knew you. Away from me, you evildoers!'
The context of this passage too seems to be one of final judgment "on that day".
I will note that the 'evildoers' never apparently offered to lift a finger to help others. They seemed to be resting secure in the "knowledge" that they were saved and possibly just judging others that they thought were not saved.
However, even in this passage, the
majority are not implied. Rather what seems to be the central focus is that of judging others harshly -- and that a Christian should not do this.
I suspect that, in the end, many athiests might be surprised to be greeting their heavenly father in heaven via the son they knew by what they did. I also suspect that some Christians will be dissapointed in their negative eternal fate.
But I don't think this is the
majority rule in either case.
If rough percentages are allowed by virtue of parables, then a 50/50 chance might be determined using parables related to the virgins using their oil unwisely.
But, then again, perhaps the fall of the angels themselves gives some indication too -- implying a third of humanity in general will fall as well.
It's not in the Scriptures, but I've thought for some time now that those of us who make it to heaven throughout all human history will probably equal the same amount as the number of angels that fell; ie., we're perhaps the replacement angels so to speak.
I don't know exactly how it will all work out in the end. But I'm fairly sure that God does.